Earthquakes occur as a result of tectonic activity. When earthquakes occur they shake the bedrock in the vicinity of the fault rupture that results in shearing stresses applied to the soil column above the rock. Pore fluid is the groundwater held within a soil or rock; namely, in the gaps between particles (i.e., in the pores). Pore water pressure refers to the pressure of groundwater held within the pores of the soil or rock.
Seismically-induced shearing forces propagate upwards through the soil profile, often resulting in damage to existing structures and sometimes resulting in soil liquefaction. Liquefaction is a phenomenon that occurs in saturated soils that involves the transfer of the effective overburden load from the soil grains to the pore fluid, with the commensurate reduction in effective stress and, hence, reduction in soil strength. In earthquake-induced liquefaction, this transfer is initiated in sandy soils by the collapse of the soil skeleton due to earthquake shaking Following liquefaction, settlement occurs as the pore water pressures dissipate. Soil liquefaction can result in billions of dollars in structural damage and can lead to a loss of life.
Many methods are available to mitigate the effects of soil liquefaction or to render the soil non-liquefiable. Deep foundations (e.g., driven pilings, drilled concrete-filled shafts) can be used to bypass the liquefiable soil and reduce the effects of liquefaction. Dynamic compaction, vibroflotation, and the installation of stone columns are some methods used to densify clean granular soils and thereby reduce liquefaction potential. Vertical stiff inclusions have also been used to absorb seismic shear stresses to reduce liquefaction potential. However, this method is partially limited in its effectiveness because the elements, if sufficiently slender, inherently are more efficient at resisting shear forces through flexure (i.e., bending) in lieu of shear.